An officer on patrol found the motorcyclist around 12:30 a.m., Livermore police Sgt. Keith Graves said.
The motorcyclist was found near the intersection of Murrieta Boulevard and Portola Avenue, police said.
Graves said the man is believed to have been traveling at a high rate of speed eastbound on Murrieta Boulevard when he may have lost control around a turn and collided with a sound wall.
The intersection was blocked off and should be reopened around 6 a.m., police said.
The cause of the accident is still under investigation and the name of the deceased man has not been released.